The present invention relates to an improved process for the homopolymerization or copolymerization of vinyl chloride. More particularly, the present invention relates to a process for preventing the adhesion of polymer to the inner walls of the polymerization tank or parts of the device with which the monomer is to be contacted during the polymerization as well as a coating agent used therefor.
In the homopolymerization of vinyl chloride or the copolymerization thereof with a monomer copolymerizable therewith (hereinafter referred to as the polymerization), the resulting polymer adheres to the inner walls of the polymerization tank and parts of the device with which the monomer is to be contacted during the polymerization operation such as reflux condenser, stirring blades, baffles and joints with pipes to cause problems such as the reduction in cooling capacity of the polymerization tank or the contamination of the vinyl chloride homopolymer or copolymer (hereinafter referred to as product) with the polymer which has been peeled off after the adhesion thereto, thereby degrading the quality of the product. Therefore, the polymerization tank has generally been cleaned each time after completion of the polymerization and before the subsequent batch in the prior art. A great deal of labor and a considerable time are required for the cleaning and, in addition, a reduction in operation rate and an increase in costs of the product are invited.
Various processes have been proposed for the prevention of the polymer from adhesion to the inner walls of the polymerization tank. However, those processes are still unsatisfactory from commercial viewpoint, since they have defects such as the retardation of polymerization velocity and deterioration of physical properties of the product, though they are effective for the prevention of the polymer adhesion.
Further, processes which do not exert an ill influence on the polymerization velocity or physical properties of the product have also been proposed. However, those processes have disadvantages that the effects of preventing the polymer adhesion are unsatisfactory. For example, U.S. Pat. No. 4,093,787 discloses a process for the polymerization of vinyl chloride wherein the reaction is carried out in a reactor having an inner wall on which there has been deposited an insoluble layer of a cross-linked polymeric material containing polar groups formed from a reaction mixture having an aldehyde as one component thereof. According to this process, the polymerization velocity is not reduced surely, since the polymeric material deposited on the wall is hardly eluted into the vinyl chloride polymerization reaction liquor because of its cross-linked structure (i.e. three-dimensional structure). It is considered that the effects of this process for the prevention of the polymer adhesion by means of a coated layer of polymeric material are obtained because the polymeric material per se acts as a radical scavenger or because the hydrophilic polymeric material makes the wall oleophobic, thereby repelling the vinyl chloride monomer. However, if the cross-linked polymeric material is used as in the process of U.S. Pat. No. 4,093,787, said effects are reduced. For example, a cross-linked condensate formed from phenol and formaldehyde known as a phenolic resin is ineffective for the prevention of the polymer adhesion, since it has neither hydrophilic properties nor radical-scavenging effect.